1. Field of the Invention
The present invention relates to a gas generator for an air bag and an air bag apparatus including two or more ignition means and two or more gas generating means for controlling discharge of gas or behavior of flow of the gas.
2. Description of Related Art
An air bag system which is mounted on various kinds of vehicles and the like including automobiles, aims to hold an occupant by means of an air bag (a bag body) rapidly inflated by a gas when the vehicle collides at a high speed to prevent the occupant from crashing into a hard portion inside the vehicle such as a steering wheel and a windscreen due to an inertia and being injured. This kind of air bag system generally comprises a gas generator actuated upon a collision of the vehicle and discharges gas, and the gas is introduced into an air bag to inflate the air bag.
It is desired that the air bag system of this type can safely restrain an occupant even when a frame of the occupant (for example, whether a sitting height of the occupant is long or short, whether the occupant is an adult or a child, and the like), a sitting attitude of the occupant (for example, an attitude of the occupant holding the steering wheel), and the like are different. Then, there has been conventionally suggested an air bag system which actuates while applying an impact as small as possible to the occupant at the initial stage of the actuation. Gas generators directed to such a system are disclosed in JP-A 8-207696, U.S. Pat. No. 4,998,751, and 4,950,458.
JP-A 8-207696 suggests a gas generator in which one igniter ignites two kinds of gas generating agent capsules to generate the gas in two stages. U.S. Pat. No. 4,998,751 and 4,950,458 suggest a gas generator in which two combustion chambers are provided for controlling actuation of the gas generator to generate gas in two stages due to an expanded flame of the gas generating agent.
However, these gas generators have drawbacks in that an internal structure thereof is complicated, a size of a container large, and a cost therefor is expensive.
Further, since the ratio between a surface area of gas generating agent, which burns at each of stages, and an area of a nozzle for controlling the combustion is not preferable over the entire stages, the internal pressure in the housing may be excessively low in the combustion of the first stage and excessively high in the combustion of the second stage, and therefore, it is not possible to control inflation of the air bag appropriately.
Further, in JP-A 9-183359 and DE-B 19620758, there is disclosed a gas generator in which two combustion chambers storing a gas generating agent are provided in a housing and an igniter is arranged in each combustion chamber, to adjust an activation timing of each of the igniters, thereby adjusting an output of the gas generator. However, in any of the gas generators, since the igniters arranged in the respective combustion chambers are independently arranged, it is difficult to assemble (manufacture), the structure itself of the gas generator becomes complicated and a volume thereof becomes large.
Accordingly, the present invention provides a gas generator which actuates while applying as small an impact as possible to an occupant at the initial stage of an actuation, and can widely and optionally adjust an output and timing of an output increase of the gas generator to safely restrain an occupant even when a frame of the occupant (for example, whether a sitting height of the occupant is long or short, whether the occupant is an adult or a child, and the like), a sitting attitude of the occupant (for example, an attitude of the occupant holding the steering wheel) and the like are different, and also can stabilize a combustion performance as well as restricting the total size of a container, having a simple structure, and being easily manufactured and lightweight.
A gas generator for an air bag of the present invention includes two or more ignition units in a housing in combination of a gas discharge port or gas discharge ports formed in the housing, and a sealing unit such as a seal tape for closing the gas discharge port. When a plurality of combustion chambers are provided in the housing, respective gas generating agents accommodated in each combustion chamber are independently ignited and burnt simultaneously or at intervals by a different ignition unit. And by controlling a diameter of the opening (opening area) of the gas discharge port and/or a thickness of the seal tape which closes the gas discharge port, it is possible to equalize the pressure (hereinafter, referred as xe2x80x9ccombustion internal pressurexe2x80x9d) in the housing when the gas generating means burns, and also to stabilize the combustion performance.
Namely, the present invention provides the gas generator for an air bag which comprises a housing forming an outer shell container and accommodating two or more ignition units to ignite upon an impact, and two or more gas generating agents which are respectively ignited and burnt by the ignition units to generate a combustion gas for inflating an air bag, and a plurality of gas discharge ports formed in the housing and closed by sealing means for maintaining an internal pressure of the housing to a given pressure, wherein a breaking pressure for breaking the sealing unit is adjusted at multiple stages by two or more gas discharge ports and/or two or more sealing units.
Preferably, a difference in the maximum internal pressures in the housing at the time of activation of the respective ignition unit is suppressed.
The breaking pressure can be adjusted by either one of an opening diameter, an opening area of the gas discharge port and the sealing units, or by a combination thereof. That is, the opening diameter can be changed between 1 and 8 mm, or 1.2 and 4 mm. With respect to the gas discharge ports being next to each other in breaking pressure for breaking the sealing units, a ratio of different breaking pressures thereof is 1.1/1 or greater, and more preferably, 4/1 to 1.1/1.
The opening area and the ratio of the opening area are changed in accordance with the amount of the gas generating agent or a surface area of the agent. The thickness of the sealing unit is changed in accordance with the ratio of the opening area or the amount of the gas generating agent or the surface area of the agent.
The amount and shape of the gas generating agent can be individually and optionally set for each of the plurality of combustion chambers. The amount of generated gas is largely varied by the number of ignitions and ignition timing. Therefore, in comparison with the generator having a single ignition unit, there exist a plurality of gas generating behavior, i.e., output characteristics, and any one of them can be selected. The combustion internal pressure depends on the ratio between the surface area of the gas generating agent and the opening area of the gas-discharge ports. When there are more than one kind of gas generating agents, the surface area of the gas generating agent, i.e., the combustion surface area is changed by the number of the ignitions and the igniting timing.
The breaking pressure is adjusted by arranging two or more kinds of opening diameters and/or opening areas of the gas discharge port. It is preferable that among two kinds or more of the gas discharge ports formed in the housing, with respect to two kinds of openings being next to each other in size of the opening diameter thereof, a ratio between the larger diameter gas discharge port and the smaller diameter gas discharge port is 4/1 to 1.1/1 and/or a ratio in opening area is 97/3 to 3/97.
Further, the breaking pressure is adjusted by arranging two or more kinds of thicknesses of the sealing unit. It is preferable that among sealing units having two kinds or more of thicknesses, with respect to the sealing units being next to each other in thickness, a thickness ratio between them is 1.1/1 to 12/1. The breaking pressure is adjusted by setting an area ratio of the two kinds or more of discharge ports having different areas that are sealed by the sealing means having two or more different thicknesses is 97/3 to 3/97. Further, in the present invention, the breaking pressure can be adjusted by arranging two or more kinds of opening diameters and/or opening areas of the gas discharge ports, and by arranging two or more kinds of thicknesses of the sealing units. Also in this case, a ratio of area of the two kinds or more of discharge ports sealed by the sealing units having two or more different thicknesses can be in a range of 97/3 to 3/97.
Further, it is preferable that the sealing unit is a seal tape comprising a seal layer having a thickness of 20 to 200 xcexcm and a bonding layer or an adhesive layer having a thickness of 5 to 100 xcexcm. In the present invention, the thickness of the seal tape includes the thickness of the seal layer and the thickness of the bonding layer or the adhesive layer. In the sealing unit such as the seal tape, the breaking pressure is adjusted by the size of the gas discharge port and/or the thickness thereof, but the maximum internal pressure in the housing at the time of combustion of the gas generating agent (hereinafter, refer to as xe2x80x9ca combustion maximum internal pressurexe2x80x9d) and the combustion performance of the gas generating agent are not adjusted.
That is, in the gas generator of the present invention, a maximum combustion internal pressure at the time of combustion of the gas generating agent is adjusted by the opening area of the gas discharge port. As a result, even after the seal tape is broken, the internal pressure in the housing can be adjusted by the relation between the opening area and the combustion performance of the gas generating agent. It is preferable that the sealing unit (especially when the sealing unit is a seal tape) includes a moisture-proof function for preventing moisture from entering the housing. In the present invention, when a constituent element which requires the moisture-proof function such as the gas generating agent is additionally provided with the moisture-proof unit, the sealing unit can be satisfactory only if the breaking pressure thereof is adjusted in multiple stages. As such an additional moisture-proof unit, in the case of the gas generating agent for example, an unit such as one enveloping with a moisture-proof sheet can be used.
In the gas generator of the present invention, a plurality of combustion chambers are provided in the housing, each of the gas generating agents for generating the combustion gas is accommodated in individual combustion chamber and independently ignited by the respective ignition unit. With this structure, a flame generated by combustion of a gas generating agent cannot be transferred to the other gas generating agent. It is preferable that the gas generating agents accommodated in the respective combustion chambers are solid gas generating agents having a different surface area per unit weight from each other. For example, when two combustion chambers accommodating the gas generating agents are provided in the housing, the combustion chambers can be concentrically provided so as to be adjacent in the radial direction of the housing, or the housing can be formed into a cylindrical shape having an axial core length longer than an outermost diameter, and the combustion chambers can be concentrically provided so as to be adjacent in the axial direction and/or a radial direction of the housing. In this case, a communication hole which allows communication between the combustion chambers can be provided. In the respective combustion chambers provided in the above way, the gas generating agents are accommodated and burnt independently. These combustion chambers are chambers exclusively used for accommodating the gas generating agents, and even if the ignition unit includes the transfer charge, the chambers can be distinguished from the space in which the transfer charge is accommodated.
The structural requirements of a dual pyrotechnic inflator according to the present invention having a plurality of openings and the equalized combustion internal pressure (the stabilized combustion performance) are that two or more ignition units and a housing for accommodating the gas generating agent are provided, the housing is provided with two or more kinds of nozzles having different opening diameter/opening area, and/or the thickness of the sealing unit which closes the gas discharge port is controlled in two ways or more. For example, the present invention is characterized in that a large nozzle and a small nozzle are formed, the large nozzle is broken at the initial stage of activation of the dual pyrotechnic inflator, i.e., by the ignition of the gas generating agent in the first chamber, and the small nozzle is opened later than, or simultaneously with the large nozzle, i.e., when the gas generating agent in the second chamber is ignited or the two igniters simultaneously ignite and the gas generating agents in both the chambers are burnt.
It is another object of the present invention to have a different charged amount of propellant (between the first chamber and the second chamber). For example, the large nozzle is opened at the internal pressure of 100 kg/cm2, and when the internal pressure reaches 150 kg/cm2 or greater, the small nozzle is also opened. In order to achieve this, it is possible to change the diameter of the nozzle of the gas discharge port while keeping the thickness of the seal tape constant, or to change the thickness of the seal tape while keeping the diameter of the nozzle constant. By controlling the diameter of the gas discharge port and/or the breaking pressure of the sealing means in the above way, for example, in a case that the two combustion chambers are provided in the housing and that the first gas generating agent and the second gas generating agent are separated and accommodated in the respective combustion chambers, combustion of any gas generating agent can be performed constantly under the ideal combustion conditions (e.g., combustion internal pressure and the like). In other words, if all of the gas discharge ports are opened at the initial stage, appropriate combustion environment can be obtained in the case of burning simultaneously the first and second gas generating agents. However, in the case of burning the second gas generating agent after about 30 milliseconds, the combustion gas of the first gas generating agent has been discharged during that period, whereby the combustion internal pressure at the time of burning the second gas generating agent becomes slightly lower as compared with the case when the two gas generating agents are burnt simultaneously, and it is not optimal combustion environment for burning the second gas generating agent. If the opening area of the gas discharge port is adjusted to be small to compensate this defect, in the case that the second gas generating agent is burnt after 10 milliseconds or 20 milliseconds, or in the case that the gas generating agents are burnt simultaneously, the pressure at combustion becomes higher. Accordingly, if one kind of gas discharge ports is opened at one time from the initial stage, it is difficult to meet all of the combustion modes. And as a result, the combustion internal pressure when the first gas generating agent is burnt is low, which brings a great difference with the internal pressure when the second gas generating agent is burnt. Thereupon, in such a gas generator, if a plurality of gas discharge ports, for example, comprising a gas discharge port opened when the first gas generating agent is burnt and a gas discharge port opened when the second gas generating agent is burnt are adjusted to be opened at different timings in accordance with the combustion of each of the gas generating agents, the gas generating agents can be burnt constantly under the ideal combustion condition (the combustion internal pressure).
Further, in the case of characteristically adjusting the actuation performance of the gas generator, particularly a change with the passage of time in the gas discharge amount, two combustion chambers are charged with the gas generating agents which are different in at least one of a burning rate, a composition, a composition ratio, and an amount from each other, respectively, and the respective gas generating agents can be independently ignited and burnt at an optional timing. Further, at each combustion chamber, the gas generating agents having a different gas amount generated at a unit time may be stored.
As the gas generating agents, in addition to an azide gas generating agent based on an inorganic azide which has been widely used, for example, a sodium azide, a non-azide gas generating agent, not based on an inorganic azide, may be used. However, from the view of safety, the non-azide gas generating agent is preferable, and as the non-azide gas generating composition, for example, a composition containing a nitrogen containing organic compound such as a tetrazole, a triazole or a metallic salt thereof and an oxygen containing oxidant such as an alkali metal nitrate, a composition using a triaminoguanidine nitrate, a carbohydroazide, a nitroguanidine and the like as a fuel and nitrogen source and using a nitrate, chlorate, a perchlorate or the like of an alkali metal or an alkaline earth metal as an oxidant, and the like may be employed. In addition, the gas generating agent can be suitably selected according to requirements such as a burning rate, a non-toxicity, a combustion temperature, and a decomposition starting temperature. In the case of using the gas generating agents having different burning rates in the respective combustion chambers, may be used the gas generating agents having the different composition or composition ratio itself, such that, for example, the inorganic azide such as the sodium azide or the non-azide such as the nitroguanidine is used as the fuel and the nitrogen source. Alternatively, the gas generating agents obtained by changing a shape of the composition to a pellet shape, a wafer shape, a hollow cylindrical shape, a disc shape, a single hole body shape or a porous body shape, or the gas generating agents obtained by changing a surface area according to a size of a formed body may be used. In particular, when the gas generating agent is formed into the porous body with a plurality of through holes, an arrangement of the holes is not particularly limited, however, in order to stabilize a performance of the gas generator, an arrangement structure such that a distance between an outer end portion of the formed body and a center of the hole and a distance between each center of the holes are substantially equal to each other is preferable. Concretely, in the cylindrical body having a circular cross section, for example, a preferred structure is such that one hole is arranged at the center and six holes are formed around the hole so that the center of each hole is the apex of regular triangles of the equal distances between the holes. Further, in the same manner, an arrangement such that eighteen holes are formed around one hole at the center may be also suggested. However, the number of the holes and the arrangement structure are determined in connection with an easiness for manufacturing the gas generating agent, a manufacture cost and a performance, and are not particularly limited.
Additionally, the housing may contain a coolant for cooling the combustion gas generated due to combustion of the gas generating agents on the side of a peripheral wall of the housing thereof. The coolant is provided in the housing for the purpose of cooling and/or purifying- the combustion gas generated due to the combustion of the gas generating agents. For example, in addition to a filter for purifying the combustion gas and/or a coolant for cooling the generated combustion gas which have been conventionally used, a layered wire mesh filter obtained by forming a wire mesh made of a suitable material into an annular layered body and compress-molding, and the like can be used. The layered wire mesh coolant can be preferably obtained by forming a plain stitch stainless steel wire mesh in a cylindrical body, folding one end portion of the cylindrical body repeatedly and outwardly to form an annular layered body and then compress-molding the layered body in a die, or by forming a plain stitch stainless steel wire mesh in a cylindrical body, pressing the cylindrical body in the radial direction to form a plate body, rolling the plate body in a cylindrical shape at many times to form the layered body and then compress-molding it in the die. Further, the coolant with a double structure with different layered wire mesh bodies at an inner side and an outer side thereof, which has a function for protecting the coolant means in the inner side and a function for suppressing expansion of the coolant in the outer side, may be used. In this case, it is possible to restrict the expansion by supporting an outer periphery of the coolant with an outer layer such as a layered wire mesh body, porous cylindrical body, and annular belt body.
And in the case of the gas generator in which the combustion gas generated due to the combustion of the gas generating agents stored in two combustion chamber reaches the gas discharge port via a different flow paths in each combustion chamber so that the gas generating agent stored in one combustion chamber is not directly ignited due to the combustion gas generated in the other combustion chambers, the gas generating agents in the combustion chambers burn in each chamber in a completely independent manner, and therefore, the gas generating agent in each combustion chamber is ignited and burnt in more secure manner. As a result, even when activation timings of two igniters are staggered significantly, the flame of the gas generating agent in the first combustion chamber ignited by the firstly actuated igniter does not burn the gas generating agent in the other combustion chamber, so that a stable output can be obtained. This kind of gas generator can be achieved, for example, by arranging a flow passage forming member in the housing to form the flow passage and introducing the combustion gas generated in the first combustion chamber to the coolant directly.
The housing mentioned above can be obtained by forming a diffuser shell having a gas discharge port or gas discharge ports and a closure shell, which forms a storing space together with the diffuser shell, with a casting, a forging, a press-molding or the like, and joining both shells. The joining of both shells can be performed by various kinds of welding methods, for example, an electronic beam welding, a laser welding, a TIG arc welding, a projection welding, and the like. Forming the diffuser shell and the closure shell by press-molding various kinds of steel plates such as the stainless steel plate makes manufacture easy and reduces a manufacturing cost. Further, forming both shells into a simple shape as cylindrical shape makes the press-molding of the shells easy. With respect to the material of the diffuser shell and the closure shell, stainless steel is preferable, and material obtained by applying a nickel plating to the steel plate is also acceptable.
In the housing mentioned above, the ignition unit actuated upon detection of an impact and ignite and burn the gas generating agent is further installed. In the gas generator according to present invention, as the ignition unit, an electric ignition type ignition unit activated by an electric signal (or an activating signal) transmitted from an impact sensor or the like which detects the impact is used. The electric ignition type ignition unit comprises an igniter activated by the electric signal transmitted from the electric sensor which exclusively detects an impact by means of an electric mechanism such as a semiconductor type acceleration sensor or the like, and a transfer charge ignited and burnt by the activation of the igniter as required.
This transfer charge should be distinguished from the gas generating agent in that the transfer charge is for burning the gas generating agent by the combustion gas thereof and not for directly inflating the air bag. When each of the two or more ignition units includes an igniter, in order to facilitate the mounting operation of the igniters, it is preferable that the respective igniters constituting the ignition unit are provided in one initiator collar to be aligned to each other in the axial direction. When the ignition unit also comprises a transfer charge ignited and burnt upon activation of the igniter, it is preferable that the transfer charge is partitioned for each igniter and independently ignited and burnt at each igniter so that flame caused by combustion of the transfer charge corresponding to any one of the igniters does not directly ignite the transfer charge corresponding to another igniter. As such a structure, for example, it is possible that each igniter is disposed in an independent igniter accommodating chamber, and the transfer charge is disposed in the igniter accommodating chamber, or the transfer charge is disposed in a position inside the independent combustion chamber where the transfer charge can be ignited and burnt. When the transfer charge is partitioned for each igniter, the respective gas generating agent accommodated in the two or more combustion chambers can be ignited and burnt by flame caused by combustion of the transfer charge in different section. And in accordance with combustion of the gas generating agent accommodated in each of the combustion chambers, any one of the plurality of gas discharge ports is opened, and thereby the gas generating agent in each of the combustion chambers can be burnt under the ideal combustion internal pressure.
The two or more ignition units disposed in the housing respectively includes the igniter activated by an electric signal, the igniters are provided in a single initiator collar so as to be aligned to each other in the axial direction, and each igniter can be arranged eccentrically with respect to the center axis of the housing. It is preferable that lead wires for transmitting the electric signals are respectively connected to the igniters, and the lead wires extend in the same direction on the same plane. Further, the lead wires are preferably connected via connectors, and the connectors are preferably arranged in the same direction on the same plane. It is preferable that the lead wires are taken out by the connector in the same direction as well as the direction perpendicular to the axial direction of the housing, and that the connector includes a positioning member having a different shape for each igniter to be connected or with projection and recess so as to be capable of connecting only one igniter.
The present invention provides a gas generator for an air bag, comprising a housing forming an outer shell container and accommodating two or more ignition units to ignite upon an impact and two or more gas generating agents which are to be independently ignited and burnt by the ignition units to generate a combustion gas for inflating an air bag, and a plurality of gas discharge ports formed in the housing and closed by a sealing unit for maintaining an internal pressure of the housing to the given pressure, wherein a first combustion chamber which starts burning first and a second combustion chamber which starts burning later are partitioned with a wall having a communication hole, the communication hole is provided with a flame-transfer-preventing unit so that the combustion is not caused in the second combustion chamber by the combustion in the first combustion chamber.
The flame-transfer-preventing unit may be a sealing member such as a seal tape or a sealing plate. The sealing member may also seal the communication hole on the side of the first combustion chamber.
Further, the present invention provides a gas generator for an air bag, comprising a housing forming an outer shell container and accommodating two or more ignition units to ignite upon an impact and two or more gas generating agents which are independently ignited and burnt by the ignition units to generate a combustion gas for inflating an air bag, and a plurality of gas discharge ports formed in the housing and closed by a sealing unit for maintaining an internal pressure of the housing to the given pressure, wherein a first combustion chamber which starts burning first is partitioned with a wall from a second combustion chamber which starts burning later, and the gases generated in the respective combustion chambers pass through the different passages and reach the gas discharge ports.
The different passages may be formed by passage-forming members.
The gas generator for the air bag mentioned above is accommodated in a module case together with the air bag (the bag body) to introduce the gas generated in the gas generator and inflate, so as to form the air bag apparatus. In this air bag apparatus, the gas generator is actuated when reacting upon the impact detected by the impact sensor, and the combustion gas is discharged from the gas discharge port in the housing. The combustion gas is flowed into the air bag, by whereby the air bag breaks the module cover to inflate, and forms a cushion for absorbing the impact between the hard member in the vehicle and the occupant.
The present invention can be realized by combining two or more structural requirements and functions described above.
The present invention provides a gas generator which has a stabilized actuation performance at all stages of actuation thereof, and actuates while applying as small an impact as possible to an occupant at the initial stage of actuation and can widely and optionally adjust an output and timing of an output increase of the gas generator to safely restrain the occupant even when frame of the occupant (for example, whether a sitting height of the occupant is long or short, whether the occupant is an adult or a child, and the like), a sitting attitude (for example, an attitude of the occupant holding the steering wheel) and the like are different.